There is a desire in the industry for higher circuit density in microelectronic devices which are made using lithographic techniques. One method of increasing the number of components per chip is to decrease the minimum feature size on the chip, which requires higher lithographic resolution. The use of shorter wavelength radiation (e.g., deep UV, e.g., 190-315 nm) than the currently employed mid-UV spectral range (e.g., 350-450 nm) offers the potential for higher resolution. However, with deep UV radiation, fewer photons are transferred for the same energy dose and higher exposure doses are required to achieve the same desired photochemical response. Further, current lithographic tools have greatly attenuated output in the deep UV spectral region.
Commercially-available lithographic positive, radiation-sensitive resist compositions generally contain an alkali-soluble phenol-formaldehyde novolac resin and an o-naphthoquinone diazide which decomposes on exposure to radiation to form an indenecarboxylic acid. Unfortunately, novolac resin and the diazide are strongly absorbing in the deep UV, especially at the lower deep UV (e.g., 193 nm), thereby making the composition unsuitable for use as a resist in the deep UV.
Reichmanis et al., "A Novel Approach to O-nitrobenzyl Photochemistry for Resists", Journal of Vacuum Science Technology, Vol. 19, No. 4, 1981, disclose a two-component deep UV resist comprising (i) a copolymer of methyl methacrylate and methacrylic acid, and (ii) a member of the family of o-nitrobenzyl carboxylates including o-nitrobenzyl cholate. Although these resists are generally transparent in the deep UV, they require high exposure doses which are unsuitable in a commercial environment.
It is therefore an object of the present invention to provide a radiation-sensitive resist composition for use in the deep UV which has improved sensitivity and resolution.
Other objects and advantages will become apparent from the following disclosure.